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Home>Products>Journal and Reviews>I.R.E.E.>Latest issue International Review of Electrical Engineering Vol. 4 N. 5-- Part A International Review of Electrical Engineering Vol. 4 N. 5-- Part B
International Review of Electrical Engineering - October 2009 - Papers Part A
International Review of Electrical Engineering - Papers- Part A
Vol. 4. n. 5, pp. 691-698
Abstract - This paper presents the design consideration and circuit implementation of an active-clamping flyback converter for PV-based LED lighting system. It can deliver the solar energy via PV cell modules to battery bank in daytime. At nighttime, the converter could also drive LED lighting system. Active clamp circuit can reduce the voltage spike on power switches due to the transformer leakage inductance when the main switch is turned off. The leakage inductance and output capacitance of switches are resonant to achieve ZVS turn-on for all switches during the commutation stage. The operation principle and system analysis of the adopted converter are discussed in detail. The prototype is presented by 50W rated power and the effectiveness of the proposed converter was verified from the experimental results. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Zero-voltage switching (ZVS), Active clamp circuit.
Vol. 4. n. 5, pp. 699-705
Abstract - This study presents two prototype flyback power supplies which are implemented using passive and active auxiliary clamp circuits. A common passive clamp is utilized to restrict power loss and voltage stress to below their corresponding reasonable level. Also, an active clamping Zero-Voltage-Switching (ZVS) additional circuit is applied to the flyback topology to enhance its performance and efficiency due to passive clamp limitations. In addition, the reliability evaluation is reckoned for two converters using a proper method to make a more accurate comparison between the converters. Because of the soft switching condition in the active-clamping ZVS flyback power supply, the main switch power loss can be reduced; it causes a decrease in junction temperature of the main switch. Therefore, an active-clamping ZVS flyback converter has less failure rate than passive clamp one. Hence, utilizing an active ZVS clamp technique in the flyback topology, the efficiency and the reliability of the flyback converter are improved despite the fact that an active clamping ZVS flyback power supply has more active and passive components. The experimental results are recorded for two flyback converter with an output voltage of 48V, an output current of 21A, and 50kHz operating frequency. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Active clamping, Flyback switched mode power supplies, Passive clamping, Reliability, Zero-voltage-switching.
by Bor-Ren Lin, Ming-Hung Yu Vol. 4. n. 5, pp. 706-714
Abstract - A parallel zero voltage switching (ZVS) converter is presented in this paper. To reduce the voltage stress of main power switch in the forward converter, active clamp based on an auxiliary switch and a clamp capacitor is adopted to recycle the energy stored in the transformer leakage inductor and magnetizing inductor. The resonant circuit based on the output capacitance of power switches and transformer leakage inductance will achieve ZVS turn-on of switches in the circuit such that the circuit efficiency is increased. The center-tapped rectifier is used at the secondary side to achieve full-wave rectifier. Instead of the conventional interleaved forward converter, the power switches in the proposed converter can achieve both functions of forward converter and active clamp at the same time. Therefore the circuit components in the power circuit are less than that of conventional interleaved forward converter. The system analysis, operation principle and design consideration of the proposed converter are presented. Finally experimental results based on a laboratory prototype are provided to verify the effectiveness of the proposed converter. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: ZVS converter, Center-tapped rectifier, Forward.
Vol. 4. n. 5, pp. 715-724
Abstract - A detailed analysis and the experimental results obtained for a non-dissipative snubber circuit optimized for parallel operation of semiconductor switches in voltage buster choppers are reported. The introduction presents a comparison of some of the non-dissipative snubber circuits including their shortages. The principle of operation is analyzed in detail by using the corresponding functional circuit diagrams and analytical expressions for particular operational phases of the snubber circuit. For practical verification the experimental results are recorded for a 1.6kW voltage boost chopper of 100kHz switching frequency and the proposed snubber circuit. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Active snubber, Boost converter, LC oscillations, Parallel operations switches.
Vol. 4. n. 5, pp. 725-729
Abstract - In this paper a new single switch Buck-Boost type dc-dc converter is introduced. This converter consists of flyback and forward transformers and only one switch in primary side and one diode in secondary side of transformers. Also this converter operates in both buck and boost modes. In this converter energy transfers to the output in both on and off switch states and controlled by PWM signal. Therefore implementation of control circuits is easy and cheap. Since this converter operates over a wide input voltage range, this converter can be employed as a power factor correction. Theoretical analysis is presented and computer simulation results verify the converter analysis. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Hard Switching, Pulse Width Modulation (PWM), Buck-Boost type, DC-DC Converter, Single Switch.
by M. F. Arman, M. K. Darwish Vol. 4. n. 5, pp. 730-743
Abstract - In recent years there has been considerable interest in the development and applications of voltage source multilevel inverters. This paper represents an overall literature review of Cascaded H-bridge Multilevel Inverter (CHB) circuit topologies with the proposal of a new topology using resonant inverters. The known and most recent topologies of CHB multilevel inverters are critically reviewed and compared. A brief overview of multilevel modulation strategies are reviewed as well. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Multilevel Inverters, Cascaded H-bridge Inverters, Hybrid multilevel topology.
Vol. 4. n. 5, pp. 744-760
Abstract - This paper introduces the average circuit models for the cascaded H-bridge (CHB) multilevel inverter for shunt compensation of electric distribution systems, such as DSTATCOMs and active filters (AFs). These CHB-based shunt compensators achieve dynamic reactive power and harmonic compensation, which is particularly appreciated for power quality (PQ) enhancement for the high-power applications. Nevertheless, digital simulation and controller synthesis of these CHB-based shunt compensators is rather complex due to the sophisticated switching topologies introduced by the pulse-width modulation (PWM) process. To simplify the difficulty for theoretical investigation and accelerate digital simulation, the state-space averaging (SSA) technique is utilized to derive the approximate model of the CHB-based inverters. The proportional-resonant (PR) controller is adopted for the current tracking control of the inverter, and the average dc-link voltage is controlled using a proportional-integral (PI) controller to regulate the active power flow of the DSTATCOM. Besides, the voltage balancing controller (VBC) is adopted to achieve equal reactive power loading among individual H-bridges by using separate PI regulators to control the difference voltage between the individual dc-link voltage and the average dc-link voltage. Extensive simulation results are presented to validate the theoretical analysis and the devised control strategies. Furthermore, the experimental results obtained from a four modules CHB-based DSTATCOM are also presented for verification. The consistency between the simulation and experimental results further verifies the validity and the effectiveness of the proposed technique. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: State-space averaging (SSA), Multilevel, Cascaded H-bridge (CHB), Voltage balancing, DSTATCOM, Active power filter.
Vol. 4. n. 5, pp. 761-768
Abstract - The paper presents results of investigation of dual-inverter-based power conversion system with synchronized pulsewidth modulation (PWM) for photovoltaic application. This system topology includes two isolated strings of photovoltaic panels, feeding two standard three-phase inverters, connected to grid by a three-phase transformer with the open winding configuration on primary side. Algorithms of synchronized PWM provide continuous voltage synchronization both in each inverter and in the load in this case. MATLAB-simulations show the behavior of dual-inverter system with continuous, two discontinuous and combined schemes of synchronized PWM. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Dual Inverters, Photovoltaic Power Conversion System, Voltage Synchronization.
Vol. 4. n. 5, pp. 769-777
Abstract - A Cascaded NPC/H-Bridge inverter is introduced as an interface in photovoltaic (PV) – Grid application. The Multilevel inverter has many advantages such as better utilization of switching devices, lower switching frequency at semiconductor, reduced harmonic content. In this paper a novel nine-level inverter is constructed from two cascaded three-level NPC/H-Bridge inverter. Compared to the classic strait forward nine level inverter, this proposed inverter requires less DC sources. This paper proposes a modified Phase Shifted PWM technique based on decomposition of the whole system into a series of four positive and negative 3-level legs. A harmonic analysis of the proposed control is carried out using double Fourier principle. Computer simulation is performed to verify the accuracy of the model and performance of the proposed model. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Cascaded NPC/H-Bridge, PV-Grid Interface, PWM Inverter, State-Space Model, Harmonic Content.
Vol. 4. n. 5, pp. 778-784
Abstract - A new pulse width modulation (PWM) technique is presented, based on Walsh functions and the novel use of harmonic injection technique for maximizing the output line fundamental voltage in the case of a three-phase inverter. A noniterative algorithm is proposed that produces a set of linear equations that relates switching angles with output voltage fundamental for given harmonic elimination constraints. The theoretical predictions are confirmed by computer simulation and DSC-based hardware implementation. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Walsh function, Three-phase inverter, Harmonic elimination, Harmonic injection.
Vol. 4. n. 5, pp. 785-791
Abstract - The improvement of power quality is a frequently discussed issue, which still requires a considerable research effort to be devoted to study of the problem. The aim of this paper arises from the quality of compensation using a shunt active power filter working under non-sinusoidal conditions. Two different cases of network current shape under non-sinusoidal conditions have been compared. The first one shows network current tracking curve of distorted voltage. And the second one shows the sinusoidal network current under non-sinusoidal voltage conditions. In the second case active power filter compensates also non-targeted non-linear loads connected to the network outside of PCC. It results in more complicated control system of shunt active power filter and it can also overload the power circuit. Finally, it results in increased demands for active power filter design. Presented experimental results verify the theoretical backgrounds. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Voltage distortion, Power quality, Power factor, ShunT active power filter.
Vol. 4. n. 5, pp. 792-798
Abstract - During the islanding mode, whenever the power grid is not available, distributed-generation (DG) produces sinusoidal output voltage and supplies nonlinear loads, thus voltage at the point of common coupling (PCC) becomes non-sinusoidal. The situation gets particularly aggravated during the islanding mode, when the power grid is not available. This deteriorates the performance of other loads connected in parallel. In this paper a scheme based on non-sinusoidal unipolar hysteresis voltage control (NSUHVC) is proposed to regulate and produce a sinusoidal voltage at the PCC. It will be demonstrated that without any current sensor or compensating device, the individual harmonic components and THD of the supply voltage at the PCC can be reduced to the desired level. Simulations have been performed to verify the viability of the proposed scheme and all of the results are presented. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Distributed generation (DG), Harmonic, Nonsinusoidal unipolar hysteresis voltage control (NSUHVC), Point of common coupling (PCC).
Vol. 4. n. 5, pp. 799-808
Abstract - An electronic pulsed power supplier for High Intensity Discharge (HID) lamps is presented in this paper. The pulsed power supplier is obtained from the integration of a two current source AC/DC converter and a full-bridge inverter. The electronic supply provides to the lamp a different current form excitation (crenels and superposition of pulses). The lamp is represented in a model of simulation by its conductance model and coupled to its electronic power supply. Finally, some experimental results from a laboratory prototype are shown and compared with simulation. The general objective of this work consists in studying the effect of a current pulsed power supply on the electric and photometric behaviour of the discharge lamps, intended in particular for photochemistry. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Gas-discharge lamps pulsed current power supply, Model conductance, Photochemistry.
Vol. 4. n. 5, pp. 809-815
Abstract - In this paper, a multi-lamp T5 digital dimming electronic ballast is developed to improve the electronic ballast in the lamp failure which is unable to clearly determine whether the lamp is good or not and the disadvantage of non-filament preheating start. It can effectively extend the lamp life of the fluorescent and has the function to protect the lamp tube from being broken down. Finally, a multi-lamp T5 digital dimming electronic ballast is designed and implemented for four 14W T5 fluorescent lamps to verify its performance. The experiment results show that this multi-lamp T5 digital dimming electronic ballast successfully lit these four T5 fluorescent lamps and has functions of filament preheating, lamp tube protection, and digital dimming control. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Fluorescent lamp, Electronic ballast, Dimming control, Microprocessor.
Vol. 4. n. 5, pp. 816-824
Abstract - This paper proposes a novel Lyapunov-based adaptive observer to estimate internal states, or fluxes, core loss, and rotor resistance of induction motor simultaneously. Traditionally, flux observers for induction motors are employed by some control algorithms, loss optimization strategies, and also torque estimators. Nevertheless, stator core loss has been generally neglected in the flux observer equations. In this paper based on the induction motor model including stator core loss resistance, a flux observer is derived. The proposed observer is capable of concurrent flux and core loss observation with online tuning of rotor resistance, while the phase currents and rotor speed are measured. The stability of the proposed observer is proved based on a Lyapunov function. Then, based on a circuit based analysis, a condition for asymptotic convergence of the estimated parameters is discussed. Experimental tests verify the validity of the proposed adaptive observer. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Flux observer, Stator core loss, Lyapunov function, Thevenin’s equivalent circuit.
Vol. 4. n. 5, pp. 825-836
Abstract - A novel identification process for three phase induction motors is presented. The linear electrical subsystem of the induction motor model using both the steady state and transient responses of the stator currents is estimated. The combination of this information is used in order to improve the reliability of the estimation process of the rotor time constant. Moreover, since only the stator currents are used no extra circuitry or sensors are required. A case study with real time results is included. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Induction motor, Offline identification, Induction motor control.
Vol. 4. n. 5, pp. 837-843
Abstract - The present paper suggests how an optimal DTC Control Algorithm applied to a propulsion system based on three-phase squirrel-cage induction motor can be achieved. The proposed approach includes a fuzzy logic controller in the DTC scheme to reduce the torque and current ripples. The electric vehicle was controlled at different operation conditions, and where the EV dynamics were taken into account. The simulation results show that the proposed controller ensures both a perfect speed control and smooth torque and current shapes with low THD, when compared to the conventional DTC scheme. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Electric vehicle, FLC based DTC scheme, Induction motors drives, NPC inverter, Torque ripple minimization.
Vol. 4. n. 5, pp. 844-850
Abstract - In this paper, discrete wavelet packet decomposition (DWPD) of induction motor current is proposed for detecting broken rotor bar conditions. Good frequency separation is essential for accurate detection of broken rotor bars since it is difficult to separate the rotor bar frequency components from the fundamental supply frequency component at rated speeds. The proposed method provides good frequency separation at a very low computational complexity. The motor current signal is first notch filtered to suppress the power system fundamental frequency. Then, the motor current is decomposed into equally spaced frequency bands by using all-pass implementation of elliptic IIR half-band filter. Next, baseline shifting of wavelet packet coefficients (WPCs) is applied to remove the filtering distortion caused by other harmonics. Finally, energy level of each frequency band is calculated by determining rms values from WPCs of associated frequency bands. The changes in the energy levels of frequency bands in which broken rotor bar related current frequencies lie are monitored to detect motor fault conditions. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Induction Motors, Wavelet Packet Decomposition, Motor Current Signature Analysis, Broken Rotor Bars.
by Miloje M. Kostic Vol. 4. n. 5, pp. 851-859
Abstract - The improvement procedure is founded on the reverse rotation test procedure for determining the stray-load loss in induction motors occurring at high frequencies (St. IEEE 112-Method E), but there is a modification and an additional test are also included. The reverse rotation test is also performed, but the higher frequencies stray-load loss values measured by the test (LLr,t) are reduced. Namely, these losses are considerably reduced owing to magnitude saturation when changing from reverse rotation test to the condition at rated voltage. The reduction factor value, for LLr,t losses, is determined on the base saturation factor measured values for fundamental and high harmonic according to the proposed procedure. For this reason, the no-load test at variable voltages is added to the standard reverse rotation test procedure. The accuracy of the proposed procedure was verified by measurements of stray-load losses in several examples, as well as on the basis of results of comparative measurements given in the literature. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Fundamental frequency stray-load loss, Higher frequencies stray-load, Reverse rotation test, Rotor removed test, Saturation factor for fundamental harmonic, Saturation factor for the higher harmonics.
Vol. 4. n. 5, pp. 860-869
Abstract - Two techniques for the control of flux switching motors in the low and high-speed ranges of operation are presented in this paper. Because of the motor construction, torque production at some rotor positions is low, which leads us into not exciting the windings in those regions. Using this method will improve the efficiency by reducing the losses but, in high-speed range of operation there exist some aspects that affect the above technique. This paper introduces the proper control strategies for flux switching motors in low and high-speed ranges of operation, and presents the simulation results. The results that are obtained based on mathematical relations and not on computer aided simulations, show the advantages of the proposed control schemes. In order to verify the current relations, experiments were performed with similar conditions. The experimental results confirm that the current relations are adequate for control purposes. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Control strategy, efficiency, Flux switching motor, Low and high speed.
Vol. 4. n. 5, pp. 870-876
Abstract - SRM drives are ideal for many industrial applications but the poor power factor of this drive makes it not desirable especially considering the cost of energy is the major concern in these days. Therefore, SRM has to comply with power quality commitments before being certified for different applications which leads to demand for high performance SRM drives. In this study, a DSP-based 8/6 SRM equipped with an asymmetrical power converter with hysteresis current controller is established and its line drawn current quality and motor driving performance are evaluated experimentally. To improvement of input current quality of this drive, two-stage power converter which uses a Current Source Rectifier(CSR) as an input stage for the asymmetrical converter of the studied SRM are proposed. Then, modeling and simulation of a 4KW, 8/6 SRM with experimental characteristics which uses a CSR as an input stage for the asymmetrical converter of the studied SRM are presented. CSR switching employs the space-vector modulation method in matrix converters. Simulation of the whole SRM drive system is performed using MATLAB-Simulink where results fully comply with required conditions such as improving power factor and THD. Usage of CSR in SRM converter input results in eliminating dc link's capacitors. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Switched Reluctance Motor (SRM), Power Factor, Current Source Rectifier (CSR), Space Vector Modulation (SVM).
Vol. 4. n. 5, pp. 877-881
Abstract - Energy efficient pump drives are realizable by using inverter fed PM synchronous motors. Because they are carry out with fractional-slot or even tooth-coil windings, the stator e.m.f. is exactly sinusoidal. For pump applications square-wave current feeding is sufficient, as the resulting load-dependent torque ripple are acceptable. The load-dependent torque ripple is calculated based on the rotating-field theory. The calculation method is approved by a comparison between simulation and measurement for an experimental machine. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Electric Machines, Permanent Magnet Machines, Servomotor, Motor Economics, Torque Ripple, Pump Drives.
Vol. 4. n. 5, pp. 882-886
Abstract - Transformer life has a considerable economic impact on the operation of an electrical network. The most important parameter in transformers life expectancy is the insulation temperature value. The variation of the temperature is described by an exponential equation based on the time constant of the system. In the thermal equivalent circuit model the time constant is equal to multiplication of thermal capacitance and thermal resistance. The aim of this paper is to present an equation for calculating thermal capacitance of oil immersed transformers that have assorted materials as conductor in their windings. In most transformers the primary and secondary windings conductor is copper, but now transformers are designed and constructed with aluminum as conductor in both primary and secondary windings, or one of them may be aluminum and the other copper. This work describes a method for calculating thermal capacitance of top-oil temperature for oil immersed transformers which is in accord with the IEEE Std C57.91-1995 Annex G, suitable for both aluminum and copper windings. The equation proposed in this work is confirmed by experimental works applied on three different oil immersed transformers. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Oil Immersed Transformers, Thermal Capacitance, Top-Oil Temperature Rise, Thermal Model.
International Review of Electrical Engineering - Papers- Part B
by A. Augugliaro, L. Dusonchet, S. Favuzza, M. G. Ippolito, E. Riva Sanseverino Vol. 4. n. 5, pp. 887-897
Abstract - In this paper, a methodology for the load flow solution of distribution systems with fixed voltage nodes (PV nodes) is presented. The proposed technique is the extension of a methodology already set up by the authors to solve distribution systems; it is an iterative approach devoted to the treatment of voltage dependent loads; at each iteration, all the network components (lines, loads, and PV nodes) are represented by resistances and reactances. The methodology is based on the identification of two networks that are solved in sequence, thus allowing the attainment of state features of the original system. One of the two systems is made up only of shunt and series resistances; the other only of shunt and series reactances. If the network is meshed, it is made radial by means of cuts and the injection of currents in the nodes created by the cuts. The unknown features are: the shunt currents in the terminal nodes of the radial or radialized system; the currents injected in the cut nodes of the meshes; and the currents injected in the shunt reactances of the PV nodes. In each of the two systems, all the unknown currents are attained by the solution of a linear system of equations in which all the coefficients of the unknowns and the known terms are deduced, with a backward process, at the branching points of the meshes, at the PV nodes, and at the source node. In the paper, after having recalled the state of the art in the backward/forward methods that are now the most commonly used for distribution systems, the methodology set up by the authors is summarized. Then the PV bus model is illustrated as well as the methodologies for the construction of the matrix of the coefficients of the unknowns and for the construction of the known terms array. Finally, the results of some applications that aim at verifying the speed of convergence and the precision of results are reported. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Backward/forward method, Distribution Networks, Power Flows.
Vol. 4. n. 5, pp. 898-906
Abstract - The novel studies have shown that Flexible AC Transmission System (FACTS) devices can greatly improve the steady state and dynamic performance of power systems. A Unified Power Flow Controller (UPFC) is the most promising device in the FACTS concept. This paper is concerned with the application of the Modal Series Method to analyze the nonlinear behavior of power systems equipped with UPFC. To do so, a general approach is developed upon which the formulation of the close loop state matrix of a power system with a UPFC is obtained. The proposed method has been applied to a typical single machine infinite bus power system (SMIB). The non linear simulation results are also presented for the example power system to validate the effectiveness of the proposed method. The results of MS method are in good agreement with those obtained from non linear simulation. Furthermore, the effect of various damping coefficients of generator on the proximity measure is examined. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Unified Power Flow Controller (UPFC), Modal Series Method, Proximity Measure.
Vol. 4. n. 5, pp. 907-913
Abstract - Presence of Distributed Generation (DG) in electric distribution systems affects the system reliability and different methods for evaluation of system reliability indices are needed. In this paper, reliability evaluation of distribution system in various operation modes of DG is attended and a new analytical method is proposed in order to evaluate system reliability indices. This method is developed based on the classification of hourly load and calculation of the restoration probability according to restoration priority of each section. This method has less calculations and accurate results, so that its accuracy is comparable to that of Monte-Carlo simulation. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Reliability, Distributed Generation, Distribution System, Analytical Method.
Vol. 4. n. 5, pp. 914-924
Abstract - Graph partitioning techniques have been widely applied in many fields in Electrical Engineering such as VLSI design, parallel processing, circuit and layout design, power system transient stability studies, intentional islanding, optimal load flow, fault estimation, dynamic security assessment, etc. The approach to the solution of each problem may be different. The objective functions in the various potential applications of graph partitioning in electrical engineering applications are also different requiring slightly different approaches to their solution. In this paper, a review of the applications of graph partitioning to electrical engineering is presented. A new approach to power system islanding is proposed using Gaussian surfaces for aggregating groups of slow coherency generators in the multilevel kernel k-means approach to partitioning in order to further speed up the calculations. Results of the application of this approach to the IEEE 30 bus power system are illustrated as a case study example. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Multilevel islanding, Spectral partitioning, Slow coherency aggregation.
Vol. 4. n. 5, pp. 925-931
Abstract - With the growth of restructured power systems, the inter area oscillations have been increased in the aggregate power systems, thus, the design of optimal stabilizer that would be more capable in damping low frequency oscillations ( LFO ) has received more interest. In this paper, the parameters of Power System Stabilizer ( PSS ), have been optimized for a Single Machine to Infinite Bus system ( SMIB ) by using evolutionary approaches including genetic algorithm(GA), particle swarm optimization(PSO), immune algorithm(IA) and hybrid algorithms. The results of optimal PSS have been compared with traditional method. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Load Frequency Oscillations (LFO), Power System Stabilizer (PSS), Single Machine to Infinite Bus System (SMIB), Immune Algorithm (IA).
Vol. 4. n. 5, pp. 932-942
Abstract - Series capacitors (SCs) are installed on long transmission lines to reduce the inductive reactance of lines. This makes it appear electrically shorter and increases the power transfer capability. Series capacitors and their associated over-voltage protection devices (typically metal oxide varistors, and/or air gaps) create several problems for protection relays and fault locators including voltage and/or current inversion, sub-harmonic oscillations, transients caused by the air-gap flashover and sudden changes in the operating reach. In this paper, an accurate fault location algorithm for series compensated power transmission lines is presented. The distance to fault is calculated from the fault loop quantities composed as for the classic fault locators, but in case of voltages additionally the compensation for the voltage drop across the bank (or banks) of series capacitors is performed. The sample fault cases and the evaluation results for the developed algorithm are presented. The fault locator simulated on a PC using PSCAD. The operating behaviour of the fault locator was assessed using a 400 kV, 400km double end fed simulated transmission line with solid and resistive single line to ground and three phase faults at various locations on the line. it relies totally on locally derived information. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Series Compensated Transmission Line, Fault Location, Distance Protection, MOV.
Vol. 4. n. 5, pp. 943-956
Abstract - The Fast Fourier Transform (FFT) suffers from the deficiency of leakage effect for the harmonic and inter-harmonic analysis of electric signals. In order to overcome the leakage effect of FFT algorithm, a new desynchronized signal processing technique is proposed, which is based on poly-item cosine window (CW) interpolation. The proposed technique is consisted of a double-stage signal processing procedure. In the first stage, the harmonic components are accurately estimated via cosine window interpolations in the frequency domain and the estimated signal is subtracted from the original signal in the time domain. In the second stage, inter-harmonic components are accurately obtained via the same interpolation without the spectral leakage problems. Since the procedure does not require synchronization, a fixed sampling frequency can be utilized to simplify the data acquisition process. Meanwhile, the computational burden is remarkably reduced due to the direct utilization of the FFT on the acquired sampling signal. Extensive simulation results are provided to verify the validity and effectiveness of the proposed algorithm, which reveals that the frequencies, amplitudes and phase angles of the harmonics and the inter-harmonics are accurately calculated, even under significant fundamental frequency deviations in the input signal. Moreover, the proposed technique is found to have overwhelming advantages in terms of the improved estimation accuracy and reduced computational burden compared to the existing unsynchronized sampling techniques in literature. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Fast Fourier Transform, Harmonic and Interharmonic detection, Leakage effect, Synchronization, Power system, Signal processing, Frequency deviation.
Vol. 4. n. 5, pp. 957-966
Abstract - This paper deals with Distribution Network reconfiguration for loss minimization. A special attention is paid to the partially meshed operation. To solve this combinatorial problem, a set of optimization methods is mandatory to overcome this problem (losses reduction and topological constraints fulfillment). After a survey of some optimization algorithms, the proposed method is described step by step. Results are presented on a real network for the partially meshed networks optimization and operation including favored customers with high reliability index. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Distribution Network (DN), Branch Exchange, Load Transfer, Graph Theory, Minimal Loss Configuration, Planar Graph, Spanning Tree, Meshed Networks.
Vol. 4. n. 5, pp. 967-975
Abstract - The electric power markets have enforced new power service quality that makes fault location in power distribution systems an obligatory issue. This paper presents a novel high impedance fault detection and location approach based on wavelet transform and artificial neural networks (ANNs). The system simulation of 20kV underground power distribution has been implemented using EMTP/ATP software. The simulated data is analyzed using advanced signal processing technique based on wavelet analysis to extract useful feature from signals and this is then applied to the artificial neural networks for locating high impedance faults in a practical underground distribution system. The paper concludes by comprehensively evaluation the performance of the technique developed in the case of high impedance faults. The results indicate that the fault location technique has an acceptable accuracy under a whole variety of different fault conditions and system parameter changing with cable ageing and altering of load taps position. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Fault location, High impedance faults, Underground distribution cable, Wavelet, Neural network.
Vol. 4. n. 5, pp. 976-984
Abstract - This paper presents a multi-stage stochastic model for short-term transmission expansion planning. Transmission planning studies deal with many uncertainties. Load uncertainty has been considered in this paper. Monte Carlo simulation method has been applied for generating scenarios. Scenario reduction techniques are used for reducing the number of scenarios. The objective function is to minimize the sum of investment costs (IC) and expected operation costs (OC). The solution technique is based on benders decomposition algorithm. Deterministic N-1 contingency criteria have been also considered. The proposed model is applied to the IEEE 24-bus Reliability Test System. The results obtained show the efficiency of the proposed method. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Benders decomposition, Monte Carlo simulation, Multi-objective optimization, Multi-stage stochastic programming, N-1 contingency criteria, Scenario reduction techniques, Transmission expansion planning, Uncertainty.
by M. Jannati, Gh. Shafiee, K. Nasri Vol. 4. n. 5, pp. 985-993
Abstract - Nearly 80% of faults in extra high voltage transmission lines are intrinsically transient. The necessity of rapid fault clearing has resulted in fast development of protection equipments. Moreover, need for reliable supply of loads has led to improvements in single phase auto-reclosing equipments. The success of the single phase auto-reclosing depends on the extinction of the secondary arc. In this paper, a novel adaptive single phase auto-reclosure is introduced. This auto-reclosure is based on the faulted phase voltage fundamental harmonic to discriminate between transient and permanent faults and also detect the extinguishing time of secondary arc.Validation of the proposed algorithm is verified via various simulations in EMTP/ATP software and experimental test. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Single Phase Auto-Reclosure, ADALINE, Transient and Permanent Fault, Secondary Arc.
by A. Laïfa, M. Boudour Vol. 4. n. 5, pp. 994-1004
Abstract - Location
of Static VAR Compensator (SVC), Thyristor Controlled Series
Compensators (TCSC) and other types of Flexible AC Transmission Systems
(FACTS) devices is important for the enhancement of practical power
systems voltage stability. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Voltage Stability, Voltage Security, FACTS location, SVC, TCSC, MOPSO.
Vol. 4. n. 5, pp. 1005-1014
Abstract - Nowadays, Wind turbines are highly used and their costs are reduced. Although using these turbines has so many benefits, but, because of their variable nature, their participating in power market has some unpredicted problems. In this paper, new approach is presented based on neural networks to forecast the production of wind power resources. This is used for probabilistic modeling of production uncertainty. Thereafter, new method is presented for bidding strategy of wind power to the power market based on minimization of imbalance cost. To determine the optimal bid to the power market, the probabilistic optimization is used. Different aspects of participation of wind generation in power market are analyzed based on the imbalanced power prices. Finally, using the practical data of a wind farm in Spain, different conditions of bidding strategy for energy is discussed. To compare the results, besides the proposed method, an advanced method for the short term prediction is used. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Wind power, Power Market, Uncertainty, Forecasting, Probabilistic optimization.
Vol. 4. n. 5, pp. 1015-1024
Abstract - This paper presents an application of intelligent algorithms to solve steady state optimal load shedding problem in electric power systems. In present study, different scenarios including system overload, critical single line and single generation outage are examined for evaluation of optimal load shedding scheme. The optimal load shedding problem is formulated as non-linear optimization problem with specific objective function subject to operation and security constraints. The objective function used in present paper consists of weighted sum of squares related to difference between connected active power loads as well as weighted sum of squares related to difference between reactive power loads in each bus bar before and after load shedding. In this paper, an attempt has been made to demonstrate comparative simulation studies for optimal load shedding issue due to weighted objective function using genetic algorithm (GA), particle swarm optimization (PSO) and ant colony system (ACS). The proposed method is tested on IEEE 30 bus system and simulation results are compared while weighting factors for objective function are provided by Analytical Hierarchy process (AHP). Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Optimal load shedding, Genetic algorithm (GA), Particle swarm optimization (PSO), Ant colony system (ACS), Analytical Hierarchy Process (AHP).
Vol. 4. n. 5, pp. 1025-1034
Abstract - Since the 80s huge efforts have been made to utilize renewable energy sources to generate electric power. Various investigations showed that generators integrated into utilities’ distribution networks could affect the host network in number of ways. This paper reports some aspects of integration of the synchronous generators into the low voltage distribution networks. An assessment of impact of the synchronous generators on the overall performances of the low voltage network in steady state and after the fault is performed. Results obtained from case study using real-life low voltage network are presented and discussed. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Power flow, Fault analysis, Reliability studies, Distributed generation.
Vol. 4. n. 5, pp. 1035-1042
Abstract - Fuses are basically simple and relatively cheap devices, although their behaviour is somewhat more complex than may be generally realised. Research is continuing on this topic with the object of producing fuses capable of meeting the ever-increasing performance demands made on them. In this paper a new concept is described and a computation of the pre-arcing time is done. The new solution has been validated by experimental tests. There is the possibility to extend the current protection range both to overloads and shortcircuits, and the Joule integral in the case of the new fuse is lower than traditional one. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Fuse, controllable fusing, Overcurrent protection, Joule integral.
Vol. 4. n. 5, pp. 1043-1052
Abstract - In this paper a simplified model for upward lightning leader inception from grounded points is presented. The critical voltage difference criterion at leader tip position is utilized to check the condition for stable leader propagation. Shielding effects of space charges are taken into account by assuming cylindrical and semi-conical volumes for leader cover and streamer zone charges. By exerting simplifying assumptions, some analytical expressions are derived to model the shielding effects of space charges. In addition to space charge effects, analytical expressions are adopted for voltage drop in leader channel. The predictions of exact physical model as well as triggered lightning measurements of ambient electrical field near stable leader inception were exploited to calibrate the model. Finally, computed stabilization field for stable leader inception and propagation is compared to the predictions of available physical and engineering models. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Lightning, Leader channel, Electric field, Breakdown.
Vol. 4. n. 5, pp. 1053-1060
Abstract - In this paper, a new approach for calculation of the magnetic forces between cylindrical coils is proposed. In this method, cross section of the coils is divided into several segments in order to calculate the magnetic force between them. The results of the calculations of the proposed method are compared with the results of the ordinary calculation method from computational time point of view. The results show the effectiveness of the former. Experiments done on constructed coils validate the precision of the proposed method. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Vector magnetic potential, Current filament technique, Cylindrical coil, Magnetic force.
Vol. 4. n. 5, pp. 1061-1068
Abstract - Nowadays, obtaining and gaining the control of energy sources are difficult and costly. Besides, most of the wars are due to energy aspects. Therefore, energy saving has now become very important for all countries in the world. Furthermore, the energy management and saving matters are adopted as fundamental policies by the governments as well. Some projects based on energy efficiency are even supported by the nonprofit foundations. Additionally, countries are exploring new energy sources and finding new techniques in using energy thrifty. The streetlights or outdoor lighting items are used up a plenty of energy in vain in some part of the day such as twilight duration because of using conventional photocell relays. Changing in the sunrise and the sunset times during the year, profiting duration from the daylight is different for each day. As the photocell relays have different inner impedance versus daylight, and the weather may be cloudy or clear, they can be turned-on early and can be turned-off lately. Besides, these relays are not so sensitive to twilight. Therefore, the amount of energy wasted during the year is going to be considerable. The duration of the consumption in vain is one hour per day at least. However, in case of using astronomical time relays, since the sunrise and the sunset times related to different time zone can be calculated during the year, all of the streetlights can be controlled by different offset time and can be saved respectable amount of energy per year. In this study, the importance of using the astronomical relays for outdoor lighting for energy saving and efficiency is discussed. The operating principal of these relays is analyzed by purposed method and compared with that of NOAA. An implementation of an astronomical time relay for Denizli City in Turkey is selected as a case study. It was proved that the energy consumption in vain one hour per day during the year is remarkable amount in the selected plot application area. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Astronomical Time Relays, Outdoor Lighting, Twilight Zone, Energy Saving and Efficiency.
Vol. 4. n. 5, pp. 1069-1075
Abstract - The transformer already connected to power system can experience saturation during the inrush transient of an incoming transformer. In the case of parallel energization, transformer can produce false differential currents that could cause relay mis-operation. In this paper sympathetic inrush phenomenon between transformers is analyzed using SIMPOW-STRI power system simulation program and laboratory transformers and a differential algorithm that is based on Artificial Neural Network (ANN) is proposed. Proposed network was trained using back-propagation algorithm. It is seen that the network is able to discriminate no-fault examples including sympathetic inrush condition from fault examples with high accuracy. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Power Transformer, Sympathetic Inrush, Fault Identification, Artificial Neural Network.
Vol. 4. n. 5, pp. 1076-1083
Abstract - This paper presents a modified topology consisting of an extra inductor and a capacitor to reduce parasitic capacitance effect related to a real inductance model for EMI attenuation in power electronic applications. The parasitic capacitance of an inductor, applied to an EMI filter, is the major limitation in high frequency components. An extra inductor is wound together with the main inductor on the same core to form a compensating transformer. To do this, simple circuit relationships between the turn ratios of the tapped compensating transformer, its parasitic capacitance and the compensating capacitor are introduced for this purpose. By these relationships, an algorithm is suggested to design the values require in practice for the transformer turn ratio and the compensating capacitor. These values are so calculated to minimize or preferably eliminate noisy capacitance effect of the main inductor. By minimizing the effect of noisy capacitor, EMI filter attenuation capability is increased. However, it is observed that although the resonance frequency will decrease, it still remains in a satisfactory level. Numerous simulations (performed by PSIM) and experimental work are performed, where they are compared accordingly with the uncompensated case. Practical outcomes are also compared with the earlier suggested topology. The comparisons well validate the proposed topology for the reduction of parasitic capacitance effect of an inductor at high frequencies. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Parasitic capacitance, EMI filter, High frequency components, Inductor model.
Vol. 4. n. 5, pp. 1084-1092
Abstract - This paper presents a new methodology for the most complex large scale unit commitment problem using agglomerative and divisive hierarchical clustering algorithms. Euclidean costs, a measure of difference in fuel cost and start-up costs of any two units are computed. On the basis of these Euclidean costs, similar type of units is placed in a cluster and accordingly different clusters are formed. This cost is also useful for preparing priority lists for the units in a cluster. The method can be broadly unfolded into three stages. First stage deals with the formation of clusters and priority list of units. Second stage presents an agglomerative hierarchical clustering algorithm that provides unit commitment solution while the load is increasing. Third stage presents a divisive hierarchical clustering algorithm that provides unit commitment solution while the load is decreasing. These algorithms search for an optimal solution that provides list of on-line units from a minimal number of clusters and cluster data points. Performance of the method is evaluated on a large scale power system consisting of 10 to 100 units in the multiples of 10 units. Input data is the standard ten thermal unit power systems for a period of 24 hours. Numerical results are presented and compared with the existing popular methods in most judicious way. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Power System operation and control, Unit Commitment Solution, Agglomerative and Divisive hierarchical Cluster Algorithms, Lambda Iteration Method.
Vol. 4. n. 5, pp. 1093-1101
Abstract - This paper presents a comparative investigation on the sensitivity of various low-wattage fluorescent lamps (FLs) used in residential and commercial lighting, during voltage sags. Based on recent testing standards and utilizing a modern industrial power corrupter and advanced photometer, extensive tests were conducted for many FLs with different ballast types. For predefined malfunction criterion of zero illuminance condition, sag depth and duration are varied to construct individual voltage immunity curves. The different ballast technologies adopted in driving the FLs seem to play a vital role in riding through in the event of voltage sag. The experimental results of tested FLs show that the lamp with electromagnetic ballast is more sensitive to voltage sags than that of the lamps equipped with electronic ballasts. Finally a method to improve the sensitivity of electronically ballasted FLs to voltage sags is implemented. This technique increases the holdup time of the dc bus voltage by connecting additional dc capacitance at the rectifier output of the ballast circuit. Details results of three 18 Watt FLs with different ballast types are presented for illustration purpose. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Fluorescent lamps, Voltage sags, Voltage tolerance curves, Ride through capability, Ballast, CFL.
Vol. 4. n. 5, pp. 1102-1109
Abstract - Active power flow in transmission lines can be controlled using a conventional Phase Shifting Transformer (PST), which introduces a phase shift between sending and receiving end voltages. However, the control of the phase shift can be executed only in steps depending on the taps available in the PST. It was verified that a Unified Power Flow Controller (UPFC) can improve transient stability and help to damp electromechanical oscillations. In this paper, an approach to obtain continuous control of the phase shift using a hybrid arrangement of conventional PST and UPFC named “Optimal Unified Power Flow Controller (OUPFC)” is presented. Operating principles and design considerations of OUPFC with PSCAD/EMTDC software package are discussed and simulated. The simulation results demonstrate the effectiveness of the OUPFC to damp electromechanical oscillations and improve the PST operation during transient condition. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: : PST, FACTS, OUPFC, UPFC, Dynamic model.
Vol. 4. n. 5, pp. 1110-1116
Abstract - A fully integrated multi-band frequency synthesizer for Inphase and Quadrature local oscillator signal generation in Digital Video Broadcasting to Handheld receivers is presented. In the proposed PLL-based integer-N synthesizer, all of the allocated frequencies for DVB tuners, in VHF, UHF and L bands, are generated. Two voltage controlled oscillators cover a frequency range of 1880-3632 MHz by using switched-capacitor banks. The VCO frequency is divided by 2, 4 and 16 to generate the quadrature signals at the synthesizer output. A fast adaptive frequency calibration block selects the closest VCO frequency to the target frequency by setting the capacitor bank control code prior to the start of phase lock. A programmable charge pump is used to reduce variations in PLL characteristics over the wide frequency range. The synthesizer has been fabricated in a 0.18um CMOS technology and the die area is 2.1×1.8 mm2. It consumes 29mA from a 1.8v power supply. Measurements show that the synthesizer quadrature output phase noise for UHF and VHF bands is lower than -83 dBc/Hz and -133dBc/Hz at 10 kHz and 1.45 MHz offset, respectively. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: DVB-H, Frequency Synthesizer, Multi band, PLL, VCO.
Vol. 4. n. 5, pp. 1117-1121
Abstract - In this article a compact ultrawideband (UWB) circular patch antenna with a novel technique for rejecting the WLAN and WiMAX bands from the UWB frequency band is presented. This method is based on applying a band notch structure instead of dual band notch system. The design of this UWB antenna is in the way that is able to reject the WiMAX band without using a filter structure and instead by introducing a semi C-shaped controllable notch band in the radiated patch which is capable of filtering the WLAN band. The proposed antenna has compact size of 22mm × 30mm. The Measurement results are in relatively good agreement with the simulations. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Ultrawideband (UWB) antenna, Band notch.
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